1. Field of the Invention
There is continuing interest in developing new, simpler and more rapid techniques to detect and measure the presence of an analyte in a sample. The analyte may be any of a wide variety of materials, such as drugs, naturally occurring physiological compounds, pollutants, chemicals, contaminants, or the like. In many cases, speed is important for the measurement, particularly with certain physiologically active compounds. In other situations, convenience can be a major consideration.
One convenient and rapid technique which has found wide application is the use of a "dip stick," generally comprising a solid rod or film which can be dipped in a sample and subsequently processed to produce a signal based on the amount of analyte in the original sample. There is ample instrumentation to measure a signal, such as light absorption, reflectance or fluorescence, of a compound bound to a solid surface. Also the dip stick allows for convenient handling, transfers, separations, and the like.
Although convenient, such techniques are highly sensitive to development time, temperature, interfering factors, reagent stability and other conditions which may affect the level of the observed signal. In performing quantitative assays where the observed signal is compared to a standard, it is necessary that the test conditions be carefully controlled to match those of the standard. Such careful control, however, detracts from the convenience of the dip stick, increases the time and cost of performing the assays, and adds to the uncertainty of the result. Moreover, the presence of interfering factors in the sample and instability of reagents are difficult to overcome even with the greatest of care.
It is therefore desirable to develop a new assay technique which provides for accurate detection of an analyte in a sample and which is largely insensitive to development time, temperature, interfering factors in the sample, reagent stability and the like.
2. Brief Description of the Prior Art
Patents concerned with various immobilized reagents and different types of test strips include U.S. Pat. Nos. 3,993,451; 4,038,485; 4,046,514; 4,129,417; 4,133,639; and 4,160,008, and German Offen. 2,636,244. Patents disclosing a variety of methods involving separations of bound and unbound antigen include U.S. Pat. Nos. Re. 29,169; 3,949,064; 3,984,533; 3,985,867; 4,020,151; 4,039,652; 4,067,959; 4,108,972; 4,145,406; and 4,168,146.